1. Field of the Invention
This invention relates to arrays of electrical transducers for radiant wave energy, and in particular, to directional arrays of microphones for multiparticipant conferences.
2. Description of the Prior Art
When one group of people wishes to confer with another group located some distance apart, one solution would be to hold a teleconference. In other circumstances, it may be desirable to put a panel discussion on a public address system. However, a suitable means of obtaining the sound signals equally well from all the members in a group while rejecting the ambient noise signals in the conference room has remained a problem for some time.
One solution to this problem is to place several microphones and loudspeakers spread about the ceiling of the conference room. A second solution is to have each talker wear a lavalier microphone around the neck, or a lapel microphone. A third solution would be to have several microphones on the conference table. All of these above solutions produce undesirable levels of noise and echo.
In 1946 C. L. Dolph (Proceedings of the I.R.E. and Waves and Electrons, Vol. 34, No. 6, June, 1946, pp. 335-348.,) suggested that an array of microphones could be used to solve this problem. He suggested that by spacing the microphones equally apart and by adjusting their sensitivities according to Chebychev polynominal coefficients, a response comprising one main lobe of given magnitude and several substantially equal sidelobes of lesser magnitude could be obtained. The level of noise transmitted by the Dolph array is lower than the noise level in any of the solutions mentioned earlier. However, since only fractions of the sensitivities of the microphones are used, the array produces a response with a signal-to-noise ratio lower than it would be if the full sensitivity of each microphone were utilized. It is desirable to have an array that could produce the response pattern suggested by Dolph and yet utilize the full sensitivities of each microphone.